One of the considerable benefits of automatic transmission is the ability to creep forward in heavy traffic by simply releasing the foot brake. In contrast, a manual transmission vehicle has to be eased gently forward under control from the accelerator, brake and clutch pedals, which quickly becomes tiresome for the driver.
Automatic transmission vehicles that are also equipped with adaptive cruise control (“ACC”) sometimes have stop/start functionality which allows the vehicle to autonomously follow the vehicle in front. In slow moving traffic ACC start/stop functionality also provides traffic crawl functionality avoiding the need for the driver to continually modulate the brake pedal to keep up with traffic. Traffic crawl functionality is not available on manual transmission vehicles because clutch, brake, and gear shifting have to be controlled by the driver.
Continuous modulation of the accelerator, brake, and clutch pedals when driving a manual transmission vehicle in heavy traffic is also not efficient from the perspective of fuel economy.
The issue of fuel economy under such conditions has been addressed by the introduction of engine start-stop technology which typically requires the transmission to be in neutral for the engine to stop for manual transmission vehicles. As a result, in a manual transmission vehicle with start-stop technology, the user not only has to control forward motion with accelerator, brake, and clutch, but also has to shift to neutral when the vehicle stops. The repeated shifting from neutral to first gear, the repeated stopping and starting of the engine and the requirement to operate accelerator, brake and clutch combine to create an unsatisfactory experience for the driver.
In addition, hybrid electric vehicles (HEVs) typically have multiple power sources, i.e. an internal combustion engine and an electric motor. The role of the electric motor differs depending on the type of hybrid vehicle.